Electrolysis of fused salts.



UNITED STATES PATENT m FRANZ VON KUGELGEN AND GEORGE O. SEWARD, OFHOL'COMBS ROCK, VIRGINIA.

ELECTROLYSIS- OF FUSED SALTS.

Specification of Letters Patent.

Patented Sept. 10, 190".

Application filed May 26, 1905. Serial No. 262,478.

-To all whom it may concern:

Improvements in the Electrolysis of Fused Salts, of

which the following is a specification.

The prevailing theory in regard to the electrolysis of a mixture offused metallic salts is that the less electro-positive metal isseparated before the more electropositive metal. This has proved to betrue for salt mixtures having the same anion. Thus, zinc is depositedfrom an electrolyte of zinc chlorid and sodium chlorid; and magnesium isseparated from an electrolyte of MgOl,'and K01, etc.

With salt mixtures where the metals are combined with different anions,the situation is different. If we have the less electro-positive metalin combination with a stronger anion than the anion of the moreelectro-positive metal, and of such a position in the table of. relativepotentials that the decomposition voltage of its compound is higher thanthe decomposition voltage of the compound of the more electro-positivemetal, the latter will be decomposed first, because the current has atendency to do the easier work first. While the anion of the moreelectro-positive metal is separated at the anode, the cation will reactin a secondary reaction with the anion of the less electro-positivemetal. Thus the result of the electrolysis would be also the separationof the less electro-positive metal from the salt mixture, if thesecondary reaction was complete; This is, however, the case only undercertain conditions, which are difficult to maintain, while, in mostcases, an alloy of both metals is obtained. A

When a fused mixture of MgGl,, NaGl, and K01,

' containing about 13 per cent. Mg, is subjected to electrolysis, we getpure magnesium. When, however, we replace most of the MgCl by MgFkeeping all other conditions the same, we get an alloy of magnesium withalkali'metals instead of pure magnesium. Electrolyzing a mixture of MgFand (121.01 results in an alloy of magnesium and calcium with constantseparation of chlorin at the anode. The results in these cases areexplained if we look at the decomposition voltages of the differentcompounds and the figures for the heat of combination. According toRichards (Aluminum,

3rd ed. pp. 234 and 237) NaOl requires for its decomposition 4.3 volts;Mgl requires 4.6 volts, and Ned? re-.

quires 4.7 volts. The reactions are,

2NaGl (electrolyzed)=2Na +20l;

MgF I-ZNa Mg+2NaF. (210,000 calories) (219,400 calories.)

S odiuni'fchlorid is decomposed first, its decomposition voltage beinglower than that of the MgF and the MgF, is in turn reduced by thesodium, though this secondary reaction is not complete because the heatof combination of 2NaF is only a little higher than that of MgF,. Theresultof electrolyzing a mixture of MgF and CaGl is similarly explained,the CaGl being decomposed before the Mg andthe MgF being reduced in asecondary reaction by the nascent calcium. The secondary reaction is notcomplete because the heat of combination of CaF is only slightly higherthan that of MgF An alloy of Mg and calcium therefore is obtained. Thesecases illustrate sufliciently .the difliculty of separating the lesselectro-positive metal from a mixed electrolyte of compounds havingdifferent anions, if the metal sought is in combination with a strongeranion than that of the more electro-positive metal. The presentinvention takes advantage of this fact in the production of alloys froma molten mixture of salts byNseIecting a compound oi the lesselectro-positive metal having a higher decomposition voltage than thecompound of the more electro-positive metal, and so regulating theelectrolytic conditions that the secondary reaction between the moreelectro-positive metal (which is set free first) and the compound of theless electro-positive metal is not complete, but takes place only to theextent necessary for the formation of the desired alloy.

The electrolyte chosen is such that what we call the moreelectro-positive metal is not only stronger as respects its own anion,but also as respects the anion of the less electro-positive m'etal thanthe less electropositive metal, so that it can reduce the compound ofanion of the more electro-positive metal is obtained at the anode.

We claim as our invention:

- 1. The production of alloys by electrolysis of a mixture of fusedmetallic salts having such combination of anions and cations that thedecomposition voltage of the compound containing the moreelectro-positive metal is lower than the decomposition Voltage of thecompound containing the less electro-positivemetal, and regulating theconditions of the electrolysis so that the secondary reaction betweenthe more electroposltive metal and the compound containing the lesselectro-positive metal is only partially complete, so that the desiredalloy is obtained.

2. The production of alloys of earth alkali metals and lesselectro-positive metals by the electrolysis of a mixture oftheir fusedsalts in which the compound containing the less electro-positive metalhas a higher decomposition voltage than the compound containing theearth-alkali metal, and regulating the electrolysis so that thesecondary reactionbetween the earth-alkali metaland the compound of theless electro-positive metal is only partlally complete,

so that the desired alloy is obtained.

7 3. The production or alloys-oi earth-alkali metals and lesselectro-posltlve metals by .the oelectrolysis of a mixture of fusedearth-alkali chlorld and 'aI-lfluorid of a less electro-,

positive metal of'higher decomposition "voltage than the earth-alkalichlorid, and regulating the electrolysis so that the secondary reactionbetween the earth-alkali metal and the fluorid is only partiallycomplete, so that the desired alloy is obtained.

4. The production of alloys of earth-alkali metals and magnesium byelectrolysis of a mixture of fused earthalkali chlorid and megnesiumfiuorid, regulatingthe electrolysis so that the secondary reactionbetween the earthalkali metal and magnesium fiuorid is only partiallycomplete. so that the desired alloy is obtained.

5. The production of magnesiumcalcium alloy by the electrolysis of afused mixture of CaCl and MgF and In witness whereof,,we have hereuntosigned our names 15 in the presence of two subscribing witnesses.

FRANZ VON KiiGE GnN. GEORGE 0. SEWARD.

Witnesses FR. VON BIDDER, .T. H. WEBB,

